The present invention is related to a wheel mounting structure having a tread portion which is limitedly permitted to rock into an improved self-aligning force transmitting relationship with a surface with which it is rollingly engaged. Advantageously, a plurality of such wheel structures may be used in a lift mast mounting arrangement of a fork lift truck.
Lift mast mounting arrangements of the type shown in U.S. Pat. No. 3,851,732 and issued to R.A. Wagner et al on Dec. 3, 1974, and assigned to the assignee of the present invention, are well known. In general, they include a first frame which is longitudinally moved within a second frame by disposing a plurality of rigidly mounted wheels or guide rollers therebetween. Unfortunately, while such lift mast mounting arrangements have been well accepted, the roller engaging rail surfaces continue to experience considerable wear and surface flasking after an extended period of operation. This is a result of a relatively small area of total contact between the hardened steel tread portion of the wheels and the rail surfaces upon which they roll. Thus, high contact stresses are generated which increases to even higher levels with distortion of the rail surface or with slight misalignment of the rigidly mounted rollers. In order to minimize these stresses, close control of the frame material has been found to be necessary, along with close control of manufacturing and assembly tolerances. Despite all these precautions, excessive wear of the roller engaging rail surfaces of the frames continues to be experienced.